1. Field of the Invention
The present invention relates to an electrode assembly for an energy storage device that includes a cross-woven arrangement of z-folded positive and negative electrodes, where the positive electrode is interwoven with the negative electrode so that a lengthwise axis of the positive electrode is perpendicular to a lengthwise axis of the negative electrode.
2. Description of the Related Art
Battery packs provide power for various technologies ranging from portable electronics to renewable power systems and environmentally friendly vehicles. For example, hybrid electric vehicles use a battery pack and an electric motor in conjunction with a combustion engine to increase fuel efficiency. Battery packs are formed of a plurality of electrochemical cells. The cells are arranged in two or three dimensional arrays and are electrically connected in series or in parallel.
Different cell types have emerged in order to deal with the space requirements of a very wide variety of installation situations, and the most common types used in vehicles are cylindrical cells, prismatic cells, and pouch cells. Regardless of cell type, each cell includes an electrode assembly that is sealed within a cell housing along with an electrolyte to form a power generation and storage unit. The electrode assembly may include an alternating arrangement of positive and negative electrode elements separated by intermediate separator plates, and can be provided in various configurations, including a stacked arrangement of individual sheets, winding an elongated electrode pair into a jelly-roll arrangement, or z-folding an elongated electrode pair into an approximation of the stacked arrangement.
The energy production volumetric efficiency of the cell, as determined by the ratio of (the volume of the electrode assembly disposed within the cell) to (the volume of the cell housing), is relatively low. For example, some cylindrical cells having a jelly-roll electrode assembly may be 80 to 90 percent volumetrically efficient, and some prismatic cells having a jelly-roll electrode assembly may be 60-75 percent volumetrically efficient. Traditionally, a prismatic or pouch type cell having a stacked arrangement of individual electrode plates can be more volumetrically efficient than one having a jelly-roll arrangement, but manufacture of the stacked arrangement is more difficult and prone to mistakes and thus more expensive than that of the jelly roll arrangement. Although z-folding addresses some manufacturing disadvantages of the stacked arrangement, some z folded electrode assemblies have relatively low energy producing capacity due to single sided application of active material to the electrode. Thus, it is desirable to increase the energy production volumetric efficiency of the cell while employing a relatively low cost electrode assembly.